C# 实体框架核心中的通用where条件

我正在构建一个使用工作单元设计模式的WebAPI应用程序。我已经创建了一个具有搜索功能的存储库：

public IQueryable<User> Search(SearchUserViewModel parameter)
{
    // Find all user from database
    var users = GetAll();

    // Id has been defined.
    if (parameter.Id != null)
        users = users.Where(x => x.Id == parameter.Id.Value);

    // Email has been defined.
    if (parameter.Email != null && !string.IsNullOrWhiteSpace(parameter.Email.Text))
    {
        var emailSearch = parameter.Email;
        switch (emailSearch.Mode)
        {
            case TextSearchMode.ContainIgnoreCase:
                // TODO: Recheck.
                users = users.Where(x => x.Email.Contains(emailSearch.Text));
                break;
            case TextSearchMode.Equal:
                users = users.Where(x => x.Email.Equals(emailSearch.Text));
                break;
            case TextSearchMode.EqualIgnoreCase:
                users = users.Where(x => x.Email.Equals(emailSearch.Text, StringComparison.OrdinalIgnoreCase));
                break;
            default:
                users = users.Where(x => x.Email.Contains(emailSearch.Text));
                break;
        }
    }

    if (parameter.Password != null && !string.IsNullOrWhiteSpace(parameter.Password.Text))
    {
        var passwordSearch = parameter.Password;
        switch (passwordSearch.Mode)
        {
            case TextSearchMode.ContainIgnoreCase:
                // TODO: Recheck.
                users = users.Where(x => x.Email.Contains(passwordSearch.Text));
                break;
            case TextSearchMode.Equal:
                users = users.Where(x => x.Email.Equals(passwordSearch.Text));
                break;
            case TextSearchMode.EqualIgnoreCase:
                users = users.Where(x => x.Email.Equals(passwordSearch.Text, StringComparison.OrdinalIgnoreCase));
                break;
            default:
                users = users.Where(x => x.Email.Contains(passwordSearch.Text));
                break;
        }
    }

    return users;
}

正如您在上面看到的代码一样，我在TextSearchMode枚举中列出了一些文本搜索模式，基于模式，我将使用Equal、EqualIgnoreCase、Contains

我正在考虑泛型函数，但我现在不知道如何创建它

---

有人能帮我吗？

不要传递user.Email，你需要传递一个Func，它定义如何从任何用户处获取所需的属性。此外，与传递

TextSearchMode

不同，您应该传递

TextSearch

对象，因为您还需要Text属性来执行搜索。下面是一个代码示例：

private IQueryable<T> SearchPropertyText(IQueryable<T> records, Func<T, string> property, TextSearch search)
{
    switch (search.Mode)
    {
        case TextSearchMode.ContainIgnoreCase:
            records = records.Where(x => property(x).Contains(search.Text));
            break;
        case TextSearchMode.Equal:
            records = records.Where(x => property(x).Equals(search.Text));
            break;
        case TextSearchMode.EqualIgnoreCase:
            records = records.Where(x => property(x).Equals(search.Text, StringComparison.OrdinalIgnoreCase));
            break;
        default:
            records = records.Where(x => property(x).Contains(search.Text));
            break;
    }
    return records;
}

---

使用泛型函数和表达式组合是可能的，但它（以及您当前的实现）可能不会像您所想的那样-例如，某些条件将转换为SQL，并取决于数据库字符串比较设置（区分大小写或不区分大小写）。而另一个将按照您的想法执行，但会在内存中执行，从而影响查询性能。

private IQueryable<T> SearchPropertyText(IQueryable<T> records, string propertyName, TextSearchMode mode)
{
    switch (mode)
    {
        case Equal:
            // TODO:
        case EqualIgnoreCase:
            // TODO:
        default:
            // TODO
    }

    return records;
}

users = SearchPropertyText(users, user.Email, emailSearch.Mode)

private IQueryable<T> SearchPropertyText(IQueryable<T> records, Func<T, string> property, TextSearch search)
{
    switch (search.Mode)
    {
        case TextSearchMode.ContainIgnoreCase:
            records = records.Where(x => property(x).Contains(search.Text));
            break;
        case TextSearchMode.Equal:
            records = records.Where(x => property(x).Equals(search.Text));
            break;
        case TextSearchMode.EqualIgnoreCase:
            records = records.Where(x => property(x).Equals(search.Text, StringComparison.OrdinalIgnoreCase));
            break;
        default:
            records = records.Where(x => property(x).Contains(search.Text));
            break;
    }
    return records;
}

users = SearchPropertyText(users, user => user.Email, emailSearch);